Lubricating oils which are utilized in internal combustion engines, and in particular, in spark-ignited and diesel engines are constantly being modified and improved to provide improved performance. Various organizations including the SAE (Society of Automotive Engineers), the ASTM (formerly the American Society for Testing and Materials) and the API (American Petroleum Institute) as well as the automotive manufacturers continually seek to improve the performance of lubricating oils. Various standards have been established and modified over the years through the efforts of these organizations. As engines have increased in power output and complexity, the performance requirements have been increased to provide lubricating oils that will exhibit a reduced tendency to deteriorate under conditions of use and thereby to reduce wear and the formation of such undesirable deposits as varnish, sludge, carbonaceous materials and resinous materials which tend to adhere to the various engine parts and reduce the efficiency of the engines.
In general, different classifications of oils and performance requirements have been established for crankcase lubricants to be used in spark-ignited engines and diesel engines because of the differences in/and the demands placed on, lubricating oils in these applications. Commercially available quality oils designed for spark-ignition engines have been identified and labeled in recent years as "SF" oils, when the oils are capable of satisfying the performance requirements of API Service Classification SF. A new API Service Classification SG has recently been established, and this oil is to be labeled "SG". The oils designated as "SG" must pass the performance requirements of API Service Classification SG which have been established to insure that these new oils will possess additional desirable properties and performance capabilities in excess of those required for SF oils. The SG oils are to be designed to minimize engine wear and deposits and also to minimize thickening in service. The SG oils are intended to improve engine performance and durability when compared to all previous engine oils marketed for spark-ignition engines. An added feature of SG oils is the incorporation of the requirements of the CC category (diesel) into the SG specification.
In order to meet the performance requirements of SG oils, the oils must successfully pass the following gasoline and diesel engine tests which have been established as standards in the industry: The Ford Sequence VE Test; The Buick Sequence IIIE Test; The Oldsmobile Sequence IID Test; The CRC L-38 Test; and The Caterpillar Single Cylinder Test Engine 1H2. The Caterpillar Test is included in the performance requirements in order to also qualify the oil for the light duty diesel use (diesel performance catetory "CC"). If it is desired to have the SG classification oil also qualify for heavy-duty diesel use, (diesel category "CD") the oil formulation must pass the more rigorous performance requirements of the Caterpillar Single Cylinder Test Engine 1G2. The requirements for all of these tests have been established by the industry, and the tests are described in more detail below.
When it is desired that the lubricating oils of the SG classification also exhibit improved fuel economy, the oil must also meet the requirements of the Sequence VI Fuel Efficient Engine Oil Dynamometer Test.
A new classification of diesel engine oil also has been established through the joint efforts of the SAE, ASTM and the API, and the new diesel oils will be labeled "CE". The oils meeting the new diesel classification CE will have to be capable of meeting additional performance requirements not found in the present CD category including the Mack T-6, Mack T-7, and the Cummins NTC-400 Tests.
An ideal lubricant for most purposes should possess the same viscosity at all temperatures. Available lubricants, however, depart from this ideal. Materials which have been added to lubricants to minimize the viscosity change with temperature are called viscosity modifiers, viscosity improvers, viscosity index improvers or VI improvers. In general, the materials which improve the VI characteristics of lubricating oils are oil soluble organic polymers, and these polymers include polyisobutylenes, polymethacrylates (i.e., copolymers of various chain length alkyl methacrylates); copolymers of ethylene and propylene; hydrogenated block copolymers of styrene and isoprene; and polyacrylates (i.e., copolymers of various chain length alkyl acrylates).
Other materials have been included in the lubricating oil compositions to enable the oil compositions to meet the various performance requirements, and these include, dispersants, detergents, friction-modifiers, corrosion-inhibitors, etc. Dispersants are employed in lubricants to maintain impurities, particularly those formed during operation of an internal combustion engine, in suspension rather than allowing them to deposit as sludge. Materials have been described in the prior art which exhibit both viscosity-improving and dispersant properties. One type of compound having both properties is comprised of a polymer backbone onto which backbone has been attached one or more monomers having polar groups. Such compounds are frequently prepared by a grafting operation wherein the backbone polymer is reacted directly with a suitable monomer.
Dispersant additives for lubricants comprising the reaction products of hydroxy compounds or amines with substituted succinic acids or their derivatives also have been described in the prior art, and typical dispersants of this type are disclosed in, for example, U.S. Pat. Nos. 3,272,746; 3,522,179; 3,219,666; and 4,234,435. When incorporated into lubricating oils, the compositions described in the '435 patent function primarily as dispersants/detergents and viscosity index improvers.